Blasting initiator



Oct. 10, 1950 R. w. CAIRNS ETAI. 2,525,397

Bms'rmc INITIATOR 2 Sheets-Sheet 1 Filed Dec. 27, 1945 FIG.

AGENT Oct. 10, 1950 RQW. CAIRNS EI'AL 2,525,397

BLASIING mrm-roa Filed Dec. 27, 1945 2 Sheets-Sheet z INVENTUkS AGENTFIG. 4

M PW" illi/l1!!! ll! 14/ FIG.

Patented Oct. 10, 1950 2,525,397 BLASTING INITIATOR Robert W. Cairns andRobert W. Lawrence, Wilmington, Del., assignors to Hercules PowderCompany, Wilmington, Del., a corporation of Delaware ApplicationDecember 27, 1945, Serial No. 637,384

Claims.

This invention relates to blasting initiators and more particularly toblasting initiators of improved initiating power.

It is well known that blasting gelatin which consists of nitroglyceringelatinized with about 7% by weight of nitrocellulose tends to becomevery insensitive on storage. This insensitiveness has usually beenassociated with the increased density which results from the gradualloss of air bubbles incorporated in the gelatin mix during manufacture.near its maximum density, i. e., between 1.58 and 1.61 g./cc., it isquite resistant to detonation by standard commercial blasting caps.However, when detonated at a high rate, high density blasting gelatinacquires a greater velocity than low density blasting gelatin and. it istherefore desirable to employ a blasting gelatin with as high a densityas possible.

When blasting gelatin of low density is detonated, it has been foundthat itwill start with a low rate of detonation (2500-3000 m./sec.) andwill then accelerate sharply to a high rate (about 7800 m./sec.). Whenblasting gelatin of high density is detonated, acceleration of a low.rate When the blasting gelatin is if a fuse cap is desired or by anignition assembly if an electric blasting cap is desired.

Having now indicated in a general way the nature of this invention,there follows a more detailed description of preferred embodimentsthereof with reference to" the accompanying drawings wherein referencesymbols refer to like parts wherever they occur and in which: A

Fig. 1 is a vertical, sectional view of a standard commercial electricblasting cap;

Fig. 2 is a vertical, sectional view of an electric blasting cap inaccordance with this invention;

Fig. 3 is a vertical, sectional view of a standard commercial fuseblasting cap; and v Fig. 4 is aivertical, sectional view of a fuseblasting cap in accordance with this invention.

The commercial'electric blasting cap of Fig. 1 includes a 0.30 calibershell I, which has an inside diameter of 0.77 cm., a bottom 0.053 cm.thick. and a wall 0.015 cm. thick. having a base charge 2 of highexplosive pressedto a density less than 1.4'5 g./cc. Superimposed uponthe base charge 2 of detonation to a high rate of detonation does notoften occur. Thus, the problem of detonating high density gelatin hasappeared to be one of producing an initial high rate of detonation. Inan effort to accomplish this, the density of the base charge in theblasting initiator has been increased, thus obtaining a high energydensity and improving its brisance. However, this expedient has notentirely solved the problem, for

even with use of such initiators insensitive blasting gelatin has, ingeneral, been detonated only at comparatively low rates or has failed topropagate detonation.

Now, in accordance with this invention, blasting initiators have beenprepared which are capable of detonating insensitive explosive materialsat a high rate. This is accomplished by employing an initiator carryinga base explosive charge of high density in a shell having a bottomweight less than the bottom weight in a standard commercial blastinginitiator or cap.

The blasting initiators or caps in accordance with this invention may beprepared employing secondary or base explosives known to the art, suchas pentaerythritol tetranitrate, nitromannite, cyclonite, mannitolhexanitrate, nitrolactose, and nitrosucrose. The explosive is placed ina shell whose bottom has a weight not more than about 0.10 gram, andpressed to a high density. A charge of priming explosive is added andthe open end of the shell closed by a capsule is aloose priming charge 3of initiating explosive. The shell is fitted with a plug 4 through whichare inserted two leg wires5. A bridge wire 6 is soldered to the legwires 5. The bridge wire 8 is embedded in the loose priming charge 3.The shell I is madewaterproof by a seal 1 composed of a waterproofingcompound, and is provided with a crimp 8 to hold a sulfur seal 9 firmlyin the shell. p

The commercial electric blasting cap vof Fig. 1 is distinguished fromthe blasting capo! Fig. 2 by the base charge 2 of greater height, due toits lower density, and the shell I with a-bottom III of greaterthickness and, accordingly, greater weight. V A

The electric blasting cap. of Fig. 2 includes a 0.30 caliber shell II,which has an nside diameter of 0.77 cm., a bottom 0.023cm. thick, and awall 0 0.015 cm. thick, havinga base charge l2 of high explosive pressedto a density more than 1.45

g./cc.

A primin charge 3, plug I, leg wires 5, bridge wire 6, seal 1, crimp 8,and sulfur seal 9 are provided for the can and consist of the samematerials applied in the same manner as described for the can de ict din Fig.1.

This electric blasting can is di tin ui hed from that of Fig. 1 andother standard commercial bla ting caps by the base charge l2 of greaterden ity, as indicated by its smaller height in the shell, and the sh llII with a bottom I 3 of reduced thickness and. accordingly, reducedweight. The commercialfuse blasting can of Fig. 3 includes a 0.22caliber shell 20, which has an inside diameter of 0.56 cm., a bottom0.043 cm. thick, and a wall 0.015 cm. thick, having a base charge 2| ofhigh explosive pressed to a density less than 1.45 g./cc. A Pr r O!1111- tiating explosive is disposed over the base charge. A gildingmetal capsule 23 with an aperture 24 therein and a wafer charge 25,respectively, are provided in the shell.

The commercial fuse blasting cap of Fig. 3 is distinguished from the capof Fig. 4 by the base charge 2| of greater height, due to its lowerdensity, and the shell 20 with a bottom 28 of greater thickness and,accordingly, greater weight.

The fuse blasting cap of Fig. 4 includes a 0.22 caliber shell 21, whichhas an inside diameter of 0.56 cm., a bottom 0.023 cm. thick, and a wall0.015 cm. thick, having a base charge 28 of high explosive pressed to adensity of more than 1.45 g./cc. A priming charge 22, capsule 23, andwafer charge 25 are provided for the cap and consist of the somematerials applied in the same manner as described for the cap depictedin Fig. 3.

This fuse blasting cap is distinguished from that of Fig. 3 and otherstandard commercial blasting caps by the base charge 12 of greaterdensity, as indicated by its smaller height in the shell, and the shell21 with a bottom 29 of reduced thickness and, accordingly, reducedweight.

The following examples illustrate the practical application of thisinvention:

EXAMPLEI Copper shells of 0.30 caliber (#6 commercial cap size) havingan inside diameter of 0.77 cm. with a 0.015 cm. wall thickness andhaving various'bottom thicknesses were charged with pentaerythritoltetranitrate pressed to various densities. These shells were furthercharged with 0.4 gram of a loose priming mixture containing 75%diazodinitrophenol and 25% potassium chlorate. A conventional ignitionassembly such as that described for Fig. 1 was provided for each shell,thus providing a complete electric blasting cap. The detonating power ofthese caps was tested as follows: A column of glycerin trinitrate wasplaced in a glass tube of 19 mm. inside diameter. The cap being testedwas inserted through a rubber stopper until the base charge was entirelysurrounded by the explosive. The cap was then initiated by a suitablesource of electric current. The detonation rate was determined by usinga high speed camera. Since both the high and the low rates arecharacteristic, approximately 7700 m./sec. for the high -rate andapproximately 1700 m./sec. for the low rate, the data in the followingtables merely show whether the rate of detonation was high (indicated byH) or low (indicated by L). The results of testing the caps of Example 1are given in Table I:

Table I 4 EXAMPLE 2 the priming explosive mixture was added and pressedat the same pressure as the priming charge. The detonating power ofthese caps were tested as follows: A column of glycerin trinitrate wasplaced in a. glass tube of 19 mm. inside diameter. The cap being testedwas inserted through a rubber stopper until the base charge was entirelysurrounded by the explosive. cap was then initiated by a. suitable fuseand the detonation rate was determined by using a high speed camera. Theresults are given in Table II:

Table II PETN BASE CHARGESCOPPER SHELLS Thickness Density of Rate ofWeight of Weight of of Bottom Charge, Detonacm Bottom, g. Charge, g.Mac. on

0. 010 0. 025 0. 25 l. 47 H 0. 010 0. 025 0. 25 1. 44 L 0. 015 0. 037 0.25 l. 48 H 0. 015 0. 037 0. 25 1. 43 L 0. 023 0. 055 0. 10 1. 65 H 0.0230. 055 0. 25 1. 52 H 0. 023 0. 055 0. 25 1.50 H 0. 035 0. 086 0.10 l. 65H 0. 035. 0. 086 0. 25 1. 48 H 0. 085 0. 086 0. 25 l. 41 L 0. 043 0. l.00 l. 69 L 0. 043 0. 105 0. 50 1. 59 L 0. 043 0.105 0. 25 l. 57 L 0. 0B0. 105 0. 20 l. 40 L EXAMPLE 3 Cellulose acetate shells of 0.22 caliberhaving an inside diameter of 0.56 cm. with a 0.076 cm. wall thicknessand having various bottom thicknesses were charged with 0.25 gram ofpentaerythritol tetranitrate pressed to various densities. These shellswere further charged with 0.3 gram of a loose priming mixture containing75% diazodinitrophenol and 25% potassium chlorate. A conventionalignition assembly such as that described for Fig. 1 was provided foreach shell, thus providing a complete electric blasting cap. Thedetonating power of these caps was determined by the same procedure asutilized for testing the caps of Example 1. The results are given inTable III:

The

Tlable III PETN BASE CHABGESCELLULOSE ACETATE SHELLS Thickness Densityof Rate of Weight of Weight of 0! 32 Bottom, g. Charge, g. 27:5 g gg 10. 064 0. 033 0. 25 1. 47 H 2 0. 0. 083 0. 25 1. 57 H 3 0. 160 0. 083 0.25 1. 40 L 4------ 0. zoo 0. 117 0. 25 l. 57 L With reference to theabove tables, it will be seen that a high rate of detonation is obtainedonly by a combination of weight of shell bottom not greater than 0.10gram and a base charge having a density greater than 1.45 g./cc. forpentaerythtritol tetranitrate. Further, it will be seen that a weight ofcharge as much as 1.00 gram pressed to a high density was ineffective togive a high rate of detonation when the weight of shell bottom wasgreater than 0.10 gram. On the other hand, a weight of charge as low as0.10 gram pressed to a high density was effective to give a high rate ofdetonation when the weight of shell bottom was less than 0.10 gram.Still further it will be seen that identical caps as to weight of bottomless than 0.10 gram and weight of charge will not give a high rate ofdetonation unless the density is above a certain minimum for a givenbase charge.

In order to determine whether the strength or weakness of the shellbottom was important, the bottoms (0.043 cm. thick) were cut oil anumber of standard #6 copper shells. The bottoms were then sealed to theshell tube with rubber cement,

producing a. very weak joint. The shells were filled with explosive asin Example 2 and the caps were tested as in Example 2. It was found thatthese caps were no more effective in producing a high rate of detonationthan standard.

#6 blasting cap shells. In other tests on copper shells, copper was cutfrom the junction of shell bottom and shell wall until it was only0.0l0'crn. thick at this junction. Even this weakening of the shell didnot result in any improvement in initiating eificiency in tests similarto the above.

Shells without bottoms are not satisfactory due to obvious handlingproblems and the impossibility of waterproofing bottomless shells.

Approximately 25% of the available energy in a 0.25 gram base charge isused in givin rapid motion to the bottom and wall shell fragments in theinitial explosive action. This corresponds to about all the energyactually available while the explosive gases are expanding to twicetheir volume. On the other hand, the energy needed to burst the shellitself it probably less than 1% of that available. It is hypothesizedthat this is why the weight of the shell bottom adjacent to the baseexplosive is of importance while the weakness or the thinness of theshell at these points is relatively unimportant.

From the examples, it is seen that the effectiveness of the blastingcaps in accordance with this invention are governed by several factors,namely, the weight of the shell bottom, the density of the base charge,and the particular base charge used. These are each interdependent.However, it is possible to fully define an operable blasting cap inaccordance with this invention by specifying only the weight of theshell bottom and the density of the base charge. The weight of basecharge ordinarily employed in commercial caps does not vary greatly andeven if varied greatly as illustrated herein does not materially affectthe rate of detonation. Ordinarily, the weight of base charge utilizedin fuse type caps is from about 0.15 to about 0.25 gram for #6, fromabout 0.5 to about 0.6 gram for #8, from about 0.9 to about 1.0 gram forArmy Engineer cap, and for electric type caps from about 0.25 to about0.40 gram for #6, from about 0.45 to about 0.55 gram for #8, from about0.9 to about 1.0 gram for Army Engineer cap. The relative detonatingpower of most common explosives is well known, hence the ranges ofweight and charge density for various base charges may be determinedfrom those of pentaerythritol tetranitrate by correction using a factorwhich represents such relative detonating power compared topentaerythritol tetranitrate.

Thus, the density of the explo -g d h;

such that it gives approximately the same strength' (explosive energyper unit volume) as pentaerythritol tetranitr'ate at a density 011.45

g./cc. For example, cyclonite, nitromannite,

mannitol hexanitrate, nitrolactos e; and nitrosucroseare"substantiallyequivalent to penta erythritol tetranitrate whenpressed to the den: sity indicated. The pressing "of various'explosives'to obtain a density that'gives auesirea bulk' strengthiswell understood in the art and is not further elaborated here.

' Therefore, in accordance with the present'inthe shell bottom should bev The weight .should be not more than about 0.10 gram, preferably fromabout 0.02 to about 0.09 gram. The base'charge utilized maybesecondary,explosives, such as" vention, the weight of as low aspractical.

pentaerythritol tetranitrate, cyclonite, Y nitro,-'

nitrosucrose, and the like.

as pentaerythritol .tetranitratef at the same den sity. Preferably,shouldhave .a density of from about 1 .50 to about 1.70g./cc.

Various priming explosives such as lead azide, silver azide, mercuryfulminate, mixturesofsul-r ,1

fur nitride with potassium chlorate or lead azide, etc., in addition todiazodinitrophenol or the diazodinitrophenol potassium chlorate mixtureshown in the examples, may be used. Materials used in the shells of thisinvention may include copper, aluminum, zinc, steel and other metals,cellulose acetate, ethyl cellulose, phenol-formaldehyde resins, andother plastics. The plugs for electric blasting caps may be formed ofsulfur, rubber or plastic materials such as phenol-formaldehyde resins,polystyrene, ethyl cellulose, porcelain, etc. If desired, the plugs maybe sealed in the caps using a sealing or waterproofing compound such assulfur, asphalt, wax, or other material. The lead wires may be of anyelectrical conductive material and may be insulated us ng enamel, cottonor plastic materials. The bridge wire connecting the terminal ends ofthe leg wires may be electrically-resistant wire composed of noble orbase metals or alloys thereof, such as platinum, Nichrome,copper-nickel, etc.

Where in the specification and appended claims the term "bottom is used,the entire base is meant, in other words, the outside diameter of theblasting cap shell at its base is equivalent to the diameter of thebottom, and the weight is determined from the area thereof times thethickness of the material forming the base times the weight of suchmaterial in grams.

The improved blasting initiators according to this invention have beenfound particularly useful for. insuring the detonating of blastinggelatin of extremely high density at its maximum rate. It thus providesfor propagation of the explosion under the severe conditions of use metin firing under high liquid heads in oil well shooting and geophysicalprospecting.

these secondary explosives. 1

What we claim and desire to protect by Letters Patent is:

1. In a blasting initiator, the combination of a shell having a bottomwhose weight is not more than 0.10 gram, and a base charge of asecondary explosive having an explosive energy per unit volumeequivalent to pentaerythritol tetranitrate at a density of 1.45 g./cc.

2. In a blasting initiator, the combination of a shell having a bottomwhose weight is from 0.02 to 0.09 gram, and a base charge of a secondaryexplosive having an explosive energy per unit volume equivalent topentaerythritol tetranitrate at a density of 1.45 g./cc.

3. In a blasting initiator, the combination of a shell having a bottomwhose weight is from 0.02 to 0.09 gram, and a base charge ofpentaerythritol tetranitrate having a density of more than 1.45 g./cc.,

4. In a blasting initiator, the combination of a shell having a bottomwhose weight is from 0.02 to 0.09 gram, and a base charge of cyclonitehaving a density of more than 1.45 g./cc.

5. In a blasting initiator, the combination of a shell having a bottomwhose weight is from 0.02 to 0.09 gram, and a base charge ofnitrolactose having a density of more than 1.45 g./cc.

6. In a blasting initiator, the combination of a shell having a bottomwhose weight is from 0.02 to 0.09 gram, and a base charge ofpentaerythritol tetranitrate having a density from 1.50'to 1.70 g./cc.

7. In a blasting initiator, the combination of a shell having a bottomwhose weight is from 0.02 to 0.09 gram, and a base charge of cyclo- 3nite having a density from 1.50 to 1.70 g./cc.

8. In a blasting initiator, the combination of a shell having a bottomwhose weight is from 0.02 to 0.09 gram, and a base charge ofnitrolactose having a density from 1.50 to 1.70 g./cc.

9. In a #6 commercial blasting cap, the combination of a shell having abottom whose weight is not more than 0.10 gram, and a base charge of asecondary explosive having an explosive energy per unit volumeequivalent to pentaerythritol tetranitrate at a density of 1.45 g./cc.

10. In a #8 commercial blasting cap, the combination of a shell having abottom whose weight is not more than 0.10 gram, and a base charge ofa*secondary explosive having an explosive energy per unit volumeequivalent to pentaerythritol tetranitrate at a density of 1.45 g./cc.

ROBERT W. CAIRNS. ROBERT W. LAWRENCE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STA'I'ES'PA'I'ENTS Number Name Date 323,524 Paulus Aug. 4, 18851,743,739 Turek Jan. 14, 1930 2,363,254 Lawrence Nov. 21, 1944 FOREIGNPATENTS Number Country Date 145,791 Great Britain Mar. 17, 1921 172,914Great Britain Dec. 22, 1921

